Filter control apparatus

ABSTRACT

In order to calculate an estimation of the quantity of accumulated particulates in a filter ( 32 ), a first estimation calculation unit ( 100 ) that outputs first estimation data (XA) calculated from the filter before and after differential pressure, and a second estimation calculation unit ( 110 ) that outputs second estimation data (XB) based on the engine operation status. Of the first and second estimation data (XA, XB), the estimation data having the higher dependability, as viewed from the engine speed at that time, is selected, whether or not to regenerate the filter is determined and with the differential between the first and second estimation (XA, XB) also taken into consideration, when the differential is larger than a prescribed value, even if the engine speed is high, the first estimation data XA is not selected since there is a risk that the dependability of the estimation value is low due to cracking of the accumulated particulates.

TECHNICAL FIELD

The present invention relates to a filter control apparatus capable ofregenerating, at a suitable timing, a filter for trapping particulatescontained in exhaust gas discharged from an engine.

BACKGROUND ART

To suppress the atmospheric diffusion of particles contained in theexhaust gas of diesel engines, in recent years, various apparatuses arebeing developed for mounting in the exhaust system of diesel engines forafter-treatment of diesel particulates in the exhaust gas. Exhaust gastreatment apparatuses of this type all include a filter for trappingparticulates contained in the exhaust gas discharged from the dieselengine. Particulates trapped by the filter gradually accumulate andultimately clog the filter, making it difficult for the exhaust gas topass through the exhaust gas passage.

Conventionally, therefore, when it is estimated that the quantity of theaccumulated particulates in the filter has reached a prescribed level,the filter is heated to elevate the filter temperature and burn theparticulates, regenerating the filter so that it again can be used totrap particulates. It is therefore desirable to carry out filterregeneration at a suitable timing, using the means of burning theparticulates by heating the filter.

Previously, wide use has been made of a filter regeneration controlarrangement in which the quantity of accumulated particulates in thefilter is estimated by measuring the before and after differentialpressure of the filter, that is, the pressure differential between theexhaust gas pressure at the inlet end of the filter and the exhaust gaspressure at the outlet end of the filter, and determining the timing ofthe filter regeneration in accordance with the estimation result.

However, the above-described conventional technology has the followingproblem points. When the engine is operating at a low speed such as whenit is idling or the like, the flow rate of the exhaust gas in theexhaust path decreases, which reduces the before and after differentialpressure of the filter even when the quantity of accumulatedparticulates is small, making it difficult to estimate accurately thequantity of the accumulated particulates on the basis of the before andafter differential pressure of the filter. Also, when the exhaust gas isin a low-pressure state, pressure sensor input/output characteristicsthat indicate the relationship between the exhaust gas pressure and thepressure sensor output signals are not linear. The precision of thepressure information possessed by the pressure sensor output signaltherefore declines, and the level of the output signal from the pressuresensor also becomes lower and susceptible to noise, so pressure sensorcharacteristics problems also make it difficult to accurately estimatethe quantity of accumulated particulates.

Furthermore, in cases such as when particulates have accumulated in thefilter and the filter continues to be in a high-temperature state whenengine operation has been stopped, volatile components released by theaccumulated particulates in the filter produces cracking in theparticulates. When such cracking occurs, exhaust gas passes through thecracked portion and inside the filter, reducing the air-flow resistanceof the filter. As a result, the before and after differential pressureof the filter becomes smaller compared to before the occurrence of thecracking, and if in this state the exhaust gas differential pressure isused to estimate the quantity of accumulated particulates, it results ina reduced estimate of the quantity of accumulated particulates, makingit difficult to accurately estimate the quantity of accumulatedparticulates.

As such, in previous apparatuses in which filter regeneration iscontrolled by measuring the before and after exhaust-gas differentialpressure of the filter, regeneration is carried out in a state in whichthere is a large amount of accumulated particulates in the filter, whichrisks causing fusing damage to the filter. Due to the difficulty ofaccurately estimating the quantity of accumulated particulates, withhigher filter regeneration frequency, there are also the problems ofdeterioration in fuel consumption and shortening of filter life.

An object of the present invention is to provide a filter controlapparatus that is able to resolve the above-described problem points ofthe conventional technology.

DISCLOSURE OF THE INVENTION

To resolve the above-described problems, in a filter control apparatusthat estimates the quantity of accumulated particulates in a filter fortrapping particulates contained in engine exhaust gas and regeneratesthe filter based on the estimation result, a filter control apparatusaccording to the present invention that estimates an accumulatedparticulate quantity based on a before and after exhaust-gasdifferential pressure of the filter and also estimates an accumulatedparticulate quantity based on engine operation status, selectivelyextracts one of these two estimation results according to engineoperation status and a result of a comparison of both estimation values,and based on the extracted estimation result, determines whether or notto carry out filter regeneration.

In a filter control apparatus that estimates the accumulated particulatequantity in a filter for trapping particulates contained in engineexhaust gas and regenerates the filter based on the estimation result,the present invention is characterized in that it includes detectionmeans for detecting the engine operation status, first estimation meansthat estimates an accumulated particulate quantity of the filter basedon a before and after exhaust-gas differential pressure of the filter,second estimation means that estimates an accumulated particulatequantity of the filter based on the engine operation status, anddifferential calculation means that calculates the differential of theaccumulated particulate quantity estimation values obtained by the firstand second estimation means, selects one of the estimation results ofthe first and second estimation means in response to the differentialcalculation means and detection means, and determines regenerationtiming of the filter in accordance with the selected estimation result.

The second estimation means can be configured to perform calculation forestimating an accumulated particulate quantity based on at least onefrom among quantity of fuel injected to the engine, the engine speed,ratio of exhaust gas recirculation in the engine, and filter beforetemperature.

The second estimation means can also be configured to carry outestimation calculation of accumulated particulate quantity, usingmapping calculation employing measured data obtained by measuringaccumulated particulate quantity increase per unit time using an actualengine.

Estimated accumulated particulate quantity values used in filterregeneration control each time the engine is stopped can be stored andthe stored accumulated particulate values used as initial values forintegration in the second estimation means.

When selecting either of the estimation results of the first and secondestimation means, sedimentary particulates can be estimated moreaccurately by calculating the amount of deviation between the twoestimation results, storing the amount of deviation as a learning valueand, in accordance with the learning value, correcting calculated valuesin the second estimation means.

In this case, a coefficient can instead be calculated in accordance withthe amount of deviation and the coefficient used to correct calculatedvalues in the second estimation means. It can be arranged so that when adeviation amount exceeds a prescribed value, the gist of that isdisplayed to the operator.

A configuration can be used whereby when the differential between thetwo estimation values when the engine is started equals or exceeds aprescribed value, the estimation result of the second estimation meansis selected regardless of the detection result of the detection means.

It can also be arranged so that the estimation result of the secondestimation means is selected within a prescribed time period regardlessof the detection result of the detection means. The time from thestarting of the engine to when the estimated accumulated particulatequantity reaches a prescribed value can be set as the prescribed timeperiod.

It can be arranged so that in cases where the differential between thetwo estimation values goes below a prescribed value, the estimationresult of the first estimation means is used instead of the estimationresult of the second estimation means.

In accordance with the above configuration, one selected from estimatedaccumulated particulate quantity value obtained based on the before andafter exhaust-gas differential pressure of the filter, and estimatedaccumulated particulate quantity value calculated from engine operationparameters or the like, is used selectively, taking into considerationthe engine operation status and the differential between the twoestimation values. The result of this is that it becomes possible toestimate the accumulated particulate quantity with higher precision,making it possible to determine a suitable filter regeneration timingwith more accuracy.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an example of an embodiment of anexhaust gas treatment apparatus equipped with the filter controlapparatus of the present invention.

FIG. 2 is a block diagram showing the configuration of the control unitshown in FIG. 1.

FIG. 3 is a block diagram showing details of the configuration of theestimation calculation unit of FIG. 2.

FIG. 4 is a flow chart for explaining the selection unit of FIG. 3.

BEST MODE OF CARRYING OUT THE INVENTION

In order to explain the present invention in greater detail, it will nowbe described with reference to the attached drawings.

FIG. 1 is an overall schematic diagram of an example of an embodiment ofthe present invention showing a case in which filter control is appliedto after-treatment of the exhaust gas of a diesel engine. Symbol 1denotes a four-cylinder diesel engine, the cylinders 2-5 of which areprovided with injectors 6-9, respectively. The operation of theseinjectors 6-9 is controlled by an engine control unit 10, using a knownarrangement to inject a required amount of high-pressure fuel, at arequired timing, into the corresponding cylinder.

An intake duct 12 connected to an intake manifold 11 is provided with aninter-cooler 13 and an air cleaner 14. An exhaust duct 16 connected toan exhaust manifold 15 is provided with an exhaust gas after-treatmentapparatus 30.

An exhaust recirculation channel 18 provided with an EGR control valve17 is provided between the intake duct 12 and the exhaust duct 16, andthe opening of the EGR control valve 17 is regulated by an actuator 19controlled by the engine control unit 10, forming an arrangement wherebypart of the exhaust gas flowing in the exhaust duct 16 can be meteredand returned to the intake manifold 11. Symbol 20 denotes an exhaustturbocharger comprised of an exhaust turbine 21 disposed inside theexhaust duct 16 and a compressor 22 that is disposed inside the intakeduct 12 and driven by the exhaust turbine 21.

The exhaust gas after-treatment apparatus 30 includes an oxidationcatalyst 31 and a filter 32 for trapping particulates, and is arrangedso that exhaust gas flowing in the exhaust duct 16 passes through thefilter 32 after passing through the oxidation catalyst 31. The oxidationcatalyst 31 is configured by forming a washcoat layer of activatedalumina on the surface of a support constituted of, for example,honeycomb-structure cordierite or heat-resistant steel, and catalystactivated components constituted of precious metal such as platinum,palladium or rhodium or the like are then imparted to the coating layer.The oxidation catalyst is configured to oxidize NO in the exhaust gas toproduce NO₂, and to also oxidize HC and CO in the exhaust gas to produceO and CO₂.

The filter 32 used is formed of porous cordierite or multiple cells ofsilicon carbide formed in parallel with cells with sealed inletsalternating with cells with sealed outlets, a so-called wallflow typehoneycomb, or is a fiber type filter comprising layers of ceramic fiberswrapped around a perforated stainless-steel tube that traps particulatesin the exhaust gas.

The inlet end (before) and outlet end (after) of the filter 32 areprovided with first and second pressure sensors 33 and 34, respectively,for detecting each exhaust gas pressure. A first pressure signal SA thatrepresents the exhaust gas pressure P1 at the inlet end of the filter 32is output from the first pressure sensor 33, and a second pressuresignal SB that represents the exhaust gas pressure P2 at the outlet endof the filter 32 is output from the second pressure sensor 34. Symbol 35denotes a flow rate sensor for detecting the flow rate of the exhaustgas flowing in the exhaust duct 16. An exhaust gas flow rate signal Ffrom the flow rate sensor 35 is input to a filter control unit 40,together with the first pressure signal SA and the second pressuresignal SB.

Instead of using the flow rate sensor 35 to detect the flow rate, theexhaust gas flow rate can be calculated from the intake air flow,injection amount, exhaust temperature, exhaust pressure. In this case,the relational expressionPV=nRT(where P: pressure, V: volume, T: temperature, nR: gas coefficient) canbe used to calculate the volumetric flow rate by calculating thevolumetric time differential.

The filter control unit 40 is used to estimate the quantity ofaccumulated particulates trapped by the filter 32 and, based on theestimation result, control the engine to regenerate the filter 32.

FIG. 2 is a block diagram showing the general configuration of thefilter control unit 40 shown in FIG. 1. The filter control unit 40 hasan estimation calculation unit 41 that performs calculations to estimatethe quantity of accumulated particulates in the filter 32 and outputsestimation value data X representing the estimation result, and aregeneration control unit 42 for controlling regeneration of the filter32 based on the estimation value data X. First pressure signal SA,second pressure signal SB, exhaust flow rate signal F and engineoperating data M representing operating conditions of diesel engine 1are input to the estimation calculation unit 41. A fuel injection amountsignal Q representing the operation status of the diesel engine 1, anengine speed signal N and a recirculation ratio signal R representingthe exhaust gas recirculation (EGR) rate are engine operating data Mthat are input from the engine control unit 10; at least one of thesesignals can be used as engine operating data M. Also input to the filtercontrol unit 40 is a temperature signal T0 representing the inlettemperature of the filter 32 that is transmitted from a temperaturesensor 36 provided at the inlet end of the filter 32.

In response to estimation data X, the regeneration control unit 42determines whether or not the accumulated particulate quantity exceedsthan a prescribed value. If according to estimation data X it isdetermined that the accumulated particulate quantity does exceed theprescribed value, a regeneration signal CS is output from theregeneration control unit 42 and input to the engine control unit 10. Inresponse to the regeneration signal CS, the engine control unit 10effects the requisite injection timing retardation control forregenerating the filter 32, effecting regeneration of the filter 32 byelevating the temperature of the exhaust gas and burning particulatesaccumulated in the filter 32.

FIG. 3 is a detailed block diagram of the estimation calculation unit41. The estimation calculation unit 41 includes a first estimationcalculation unit 100 that estimates the accumulated particulate quantityof the filter 32 from the before and after differential pressure of thefilter 32, and a second estimation calculation unit 110 that estimatesthe accumulated particulate quantity of the filter 32 based on theoperation status of the diesel engine 1, and uses a selection unit 120to select the calculation output of either the first estimationcalculation unit 100 or the second estimation calculation unit 110,which is then output as the estimation value data X.

The first estimation calculation unit 100 has a differential pressurecalculation unit 101 that, in response to the first and second pressuresignals SA, SB, calculates the exhaust-gas differential pressure (filterbefore and after differential pressure) ΔP between the inlet and outletends of the filter 32 trapping particulates, and a flow rate calculationunit 102 that, based on the exhaust flow rate signal F from the flowrate sensor 35, calculates the flow rate FL of the exhaust gas flowingin the filter 32. The output of the differential pressure calculationunit 101 and the output of the flow rate calculation unit 102 are inputto a division unit 103, and in the division unit 103, calculations arecarried out to obtain the value of ΔP/FL. The flow rate calculation unit102 can also be configured to calculate the flow rate FL by using theoperation parameters of the diesel engine 1, as has been alreadyexplained.

The result of the calculation by the division unit 103 is input to afirst accumulated quantity calculation unit 105 via a digital filter104, and based on the value of ΔP/FL, the first accumulated quantitycalculation unit 105 calculates an estimated value of the accumulatedparticulate quantity at that time. The result of the estimationcalculation obtained by the first accumulated quantity calculation unit105 is output as first estimation data XA.

An example of the configuration of the first estimation calculation unit100 has been described in the foregoing. However, the technique of usingthe filter before and after differential pressure as a basis forcalculating an estimate of the quantity of accumulated particulates in afilter is a publicly known one, so the configuration of the firstestimation calculation unit 100 shown in FIG. 3 can be replaced byanother publicly-known configuration.

The second estimation calculation unit 110 will now be explained. Thesecond estimation calculation unit 110 is configured as a means forcalculating an estimation of the accumulated particulate quantity in thefilter 32, based on the operation status of the diesel engine 1. Thesecond estimation calculation unit 110 has a second accumulated quantitycalculation unit 111 for calculating an estimation of the accumulatedparticulate quantity in the filter 32, per unit time, based on operatingcondition data. In this embodiment, the second accumulated quantitycalculation unit 111 is configured to use the fuel injection amountsignal Q, engine speed signal N and recirculation ratio signal R as abasis for calculating an estimated value ΔY of the accumulatedparticulate quantity per unit time concerned.

When the temperature of the filter 32 rises in conjunction with the risein the exhaust gas temperature, particulates accumulated therein areburned, decreasing the accumulated particulates. That is, a filter 32regeneration operation is carried out. Symbol 112 denotes a regenerationamount calculation unit 112 that in accordance with the operatingcondition of the diesel engine 1, calculates an estimated value of theamount by which the accumulated particulates are reduced by the burning,which is taken as the amount of the regeneration. In response to thefuel injection amount signal Q, the engine speed signal N, therecirculation ratio signal R, the temperature signal T0, and secondestimation data XB obtained as described below, the regeneration amountcalculation unit 112 is configured to calculate as an estimatedregeneration amount value ΔZ, an estimation of the amount of accumulatedparticulates in the filter 32 burned per unit time.

The estimated value ΔY of the accumulated particulate quantity per unittime from the second accumulated quantity calculation unit 111, and theestimated regeneration amount value ΔZ per unit time from theregeneration quantity calculation unit 112, are transmitted to anintegration calculation unit 113 as accumulation data DY andregeneration data DZ, respectively. From the selection unit 120, initialvalue data ID representing initial integration values are input to theintegration calculation unit 113. The initial value data ID usesestimation value data X values stored in the selection unit 120 at thetime of the most recent engine shutdown, as described below. In theintegration calculation unit 113, using this initial value data ID,accumulation data DY and regeneration data DZ are subjected to timeintegration processing at the illustrated polarity. The integrationcalculation result obtained in the integration calculation unit 113 isthe result of the estimation calculation in the second estimationcalculation unit 110. That is, second estimation data XB representing anestimate of the accumulated particulate quantity in the filter 32calculated from the operation status of the diesel engine 1, is outputfrom the integration calculation unit 113.

As described, the second estimation data XB is also input to theregeneration quantity calculation unit 112, which is configured tocalculate an estimated regeneration amount value ΔZ per unit time basedon the fuel injection amount signal Q, the engine speed signal N, therecirculation ratio signal R, the temperature signal T0 and the secondestimation data XB. The reason for taking the second estimation data XBinto consideration in the estimation calculation by the regenerationquantity calculation unit 112 is that, even when exhaust gas temperatureand other such conditions are identical, the regeneration amount isaffected by the quantity of accumulated particulates at that time, sothe effect is taken into consideration for a more precise estimation ofthe regeneration amount.

Also, the respective calculations by the first accumulated quantitycalculation unit 105, second accumulated quantity calculation unit 111and regeneration quantity calculation unit 112 can be implemented asmapping calculations, in which case, by using an actual engine with afilter, setting the prescribed test-bench input conditions beforehandand measuring the accumulated quantity and regeneration amount, themapping data used in each case can be suitably set based on the resultsof the measurements.

The selection unit 120 is configured to select either one of firstestimation data XA and second estimation data XB, taking intoconsideration diesel engine 1 operation status and the differentialbetween first estimation data XA and second estimation data XB, andoutput the selected estimation data as estimation data X representing anestimated value of the quantity of accumulated particulates in thefilter 32 at that time.

In this embodiment, engine speed signal N is input to the selection unit120 as a signal representing the operation status of the diesel engine1.

FIG. 4 is a flow chart for explaining the configuration and operation ofthe selection unit 120. The selection unit 120 is described below, withreference to FIG. 4. First, in step S1, the engine speed signal N isused to determine whether or not engine speed EN is greater than aprescribed value Ne. The prescribed value Ne represents the lower limitof an engine speed that enables the accumulated particulate quantity tobe correctly estimated from the before and after differential pressureof the filter 32. The idling speed, for example, can be set as theprescribed value Ne.

If the engine speed EN is not above the prescribed value Ne, thedetermination result of step S1 is NO, and the process enters step S2,where second estimation data XB is selected as estimation data X. On theother hand, when the engine speed is greater than the prescribed valueNe, the determination result of step S1 is YES and the process advancesto step S3.

In step S3, first estimation data XA and second estimation data XB arecompared to determine whether or not the absolute value ΔM of thedifferential thereof is greater than prescribed value K. In the case ofΔM>K, it is possible that ΔM has become large due to the occurrence ofcracking in the accumulated particulates in the filter, and thedependability of the first estimation data XA value is determined to below. Therefore, if the determination result of step S3 is YES, theprocess advances to step S2, and second estimation data XB is selectedand output as estimation data X. On the other hand, in the case of ΔM□K,the determination result of step S3 is NO, and the process advances tostep S4.

In step S4, it is determined whether or not the quantity of particulatesthat has accumulated since the diesel engine 1 was started that time hasreached a prescribed quantity that is sufficient to repair cracking. Theconfiguration here compares the second estimation data XB value at thetime of the most recent engine shutdown with the current secondestimation data XB value to determine whether or not the currentaccumulation quantity is a prescribed quantity or more.

Even when the determination result of step S3 is NO, if the currentaccumulation quantity is not a prescribed quantity or more, thedetermination result of step S4 is NO, and the process advances to stepS2 and second estimation data XB is selected. On the other hand, if thecurrent accumulation quantity is a prescribed quantity or more, thedetermination result in step S4 is YES, and the process enters step S5,where first estimation data XA is selected.

In this way, in cases where the engine speed EN is less than theprescribed value Ne, the second estimation data XB is selected as beingmore dependable than the first estimation data XA.

Also, when the absolute value ΔM of the differential between firstestimation data XA and second estimation data XB is greater than K, itis possible that the main factor is the occurrence of cracking in theaccumulated particulates in the filter, so in this case too, secondestimation data XB is selected as being more dependable.

Even when the determination result of step S3 was ΔM□K, during theperiod in which the current accumulation quantity does not reach orexceed the prescribed value, just in case the process enters step S2,and second estimation data XB is selected.

As the accumulated particulate quantity increases with the passage oftime from the starting of the engine and the determination result ofstep S4 becomes YES, first estimation data XA is selected for the firsttime.

After either first estimation data XA or second estimation data XB hasthus been selected, the process enters step S6, where it is determinedwhether or not the engine has stopped. If the diesel engine 1 has notyet stopped, the determination result in step S6 is NO, the processreturns to step S1 and the above-described operation is repeated.

When operation of the diesel engine 1 is stopped, such as by turning theignition key to OFF, in step S6 the determination result becomes YES,and in step S7, the estimation data X value at this time is stored inmemory 120A as initial value data ID, and the operation ends.

However, because integration calculations are performed in the case ofthe estimation calculations carried out in the second estimationcalculation unit 110, it can be foreseen that over the long term,calculation results will become inaccurate due to cumulative error. Thisbeing the case, in the example of the embodiment shown in FIG. 3, thesecond estimation calculation unit 110 is provided with a correctionamount storage unit 114 and a correction value calculation unit 115,forming a configuration whereby the quantity of accumulated particulatesper unit time calculated by the second accumulated quantity calculationunit 111 is appropriately corrected by means of a learning operation.

That is, in a case in which first estimation data XA and secondestimation data XB are input to the correction value calculation unit115 and the selection unit 120 has selected second estimation data XB,and the speed of the diesel engine 1 is elevated and the selection unit120 carries out a data switching operation to select first estimationdata XA in place of second estimation data XB, in response to thisswitchover operation, the differential between the first estimation dataXA and the second estimation data XB at this time is calculated asfollows.

When regeneration processing is not being carried out and theregeneration process integration value is zero, if the differential iswithin a prescribed range, the ratio DXA/DXB between estimation valueDXA derived from the first estimation data XA and estimation value DXBderived from the second estimation data XB is calculated as a deviationcoefficient C, and the deviation coefficient C is stored in thecorrection amount storage unit 114.

If in either case the above differential exceeds the prescribed range,it is determined that the filter is degraded, and the above deviationcoefficient C is not calculated. In cases where it is thus determinedthat a filter is degraded, it is desirable to use a configurationwhereby a warning is displayed by predetermined means such as a lampthat comes on or flashes to urge the operator to replace the filter.

The deviation coefficient C is stored in the correction amount storageunit 114 as a learning value and transmitted as a learning value to thesecond accumulated quantity calculation unit 111, where the accumulatedparticulate quantity per unit time calculated therein is corrected bybeing multiplied by the deviation coefficient C, after which thecorrected accumulated particulate quantity per unit time output as theestimated value ΔY of the accumulated particulate quantity per unittime.

In this way, in the correction value calculation unit 115 firstestimation data XA and second estimation data XB values are used tocalculate the deviation coefficient C, the deviation coefficient C isstored in the correction amount storage unit 114, and by appropriatelycarrying out corrections in the course of calculation processing carriedout to calculate the accumulated particulate quantity per unit time,errors in the integration calculations by the integration calculationunit 113 are corrected and do not accumulate. As a result, the secondestimation data XB, which is estimation data based on the quantity ofaccumulated particulates per unit time, becomes a value that hasdependability, so accumulated particulate quantity estimations areaccurate.

Thus, with this configuration, when either one of the estimation resultsof the first and second estimation calculation units is selected, thedeviation amount of the two estimation results is calculated and thedeviation amount is stored as a learning value, so that by correctingvalues calculated in the second estimation calculation unit inaccordance with this learning value, the accumulated particulatequantity is estimated with more accuracy.

The filter control unit 40 is configured as in the above, so that of twoestimation values, comprised by an accumulated particulate quantityestimation value calculated on the basis of the filter before and afterdifferential pressure, and a simulated accumulated particulate quantityestimation value based on the operation status of the diesel engine 1,the estimation value having the higher dependability according to thestatus at that time is selected. And, whether or not to regenerate thefilter 32 is determined in accordance with the estimation value thusselected, so regeneration of the filter 32 can be implemented at ahighly appropriate timing. As a result, compared to previously, the lifeof the filter 32 can be extended, so it can be expected that runningcosts can be reduced.

As described in the foregoing, of two estimation values, which are anaccumulated particulate quantity estimation value calculated based onthe filter before and after differential pressure, and a simulatedaccumulated particulate quantity estimation value based on accumulatedparticulate quantity per unit time, the estimation value having thehigher dependability according to the engine operation status at thattime is selected, and whether or not to regenerate the filter isdetermined in accordance with the estimation value thus selected, soregeneration of the filter can be implemented at a highly appropriatetiming. As a result, the filter regeneration frequency can be optimizedand the life of the filter can be extended compared to before, so it canbe expected that running costs can be reduced.

INDUSTRIAL APPLICABILITY

As set out in the foregoing, the filter control apparatus of the presentinvention is useful for regenerating filters at a suitable timing.

1. In a filter control apparatus that estimates an accumulatedparticulate quantity in a filter for trapping particulates contained inengine exhaust gas and regenerates the filter based on the estimationresult, a filter control apparatus that includes detection means fordetecting the engine operation status, first estimation means thatestimates an accumulated particulate quantity of the filter based on abefore and after exhaust-gas differential pressure of the filter, secondestimation means that estimates an accumulated particulate quantity ofthe filter based on the engine operation status, selecting means thatselects either of the estimation results of the first and secondestimation means in response to the differential calculation means anddetection means, and means that, when selecting either of the estimationresults of the first and second estimation means, calculates deviationamount between the two estimation results, stores the deviation amountbetween the two estimation results, stores the deviation amount as alearning value, calculates data for correcting the second estimationmeans in accordance with the learning value and supplies the data to thesecond estimation means, and determines regeneration timing of thefilter in accordance with the selected estimation result selected by theselecting means.
 2. A filter control apparatus as claimed in claim 1,wherein in the second estimation means, calculation is carried out forestimating an accumulated particulate quantity based on at least onefrom among quantity of fuel injected to the engine, engine speed, ratioof exhaust gas recirculation in the engine, and filter beforetemperature.
 3. A filter control apparatus as claimed in claim 1,wherein in the second estimation means, estimation calculation ofaccumulated particulate quantity is carried out using mappingcalculation employing measured data obtained by measuring accumulatedparticulate quantity increase per unit time using an actual engine.
 4. Afilter control apparatus as claimed in claim 3, wherein the secondestimation means is configured to obtain estimated values of accumulatedparticulate quantity in the filter by integrating data obtained by themapping calculation.
 5. A filter control apparatus as claimed in claim4, wherein estimated values of accumulated particulate quantity used infilter regeneration control each time the engine is stopped are storedand the stored accumulated particulate values are used as initial valuesfor integration in the second estimation means.
 6. A filter controlapparatus as claimed in claim 1, wherein a coefficient is calculated inaccordance with the amount of deviation and the coefficient is used tocorrect calculated values in the second estimation means.
 7. A filtercontrol apparatus as claimed in claim 1, wherein when the deviationamount exceeds a prescribed value, a gist thereof is displayed to theoperator.
 8. A filter control apparatus as claimed in claim 1, whereinwhen the differential when the engine is started equals or exceeds aprescribed value, the estimation result of the second estimation meansis selected regardless of the detection result of the detection means.9. A filter control apparatus as claimed in claim 1, wherein when thedifferential when the engine is started equals or exceeds a prescribedvalue, the estimation result of the second estimation means is selectedwithin a prescribed time period regardless of the detection result ofthe detection means.
 10. A filter control apparatus as claimed in claim9, wherein the prescribed time period is a period of time from thestaffing of the engine to a time at which estimated accumulatedparticulate quantity estimated from the staffing of the engine reaches aprescribed value.
 11. A filter control apparatus as claimed in claim 8,wherein in a case in which the differential has become smaller than aprescribed value, an estimation result of the first estimation means isused instead of an estimation result of the second estimation means.